Gym bunny, earth mother, lady of the manor, material girl and scourge of the Catholic church; if one of Madonna's reinventions doesn't inspire you, there are plenty more. But while her multiple faces might seem calculating one thing she has never tried to tinker with is her own strength.

No matter the decade or the fashion, she has always been frank about her toughness and ambition. People may sneer at her muscular arms, but they miss the point – Madonna is about power. She is still one of the most famous women on the planet, despite nearly 30 years in a notoriously fickle business, and compared with her contemporaries – Michael Jackson and Prince – has remained in the spotlight largely on her own terms.

She inspires not because she gives other women a helping hand, but because she breaks the boundaries of what's considered acceptable for women – talking openly about her desires, refusing to pretend to be gentle, taking younger lovers, allowing her physical strength to be seen, still presenting herself as sexual at 52. The outrage, derision and "how dare she" comments that follow her every move are testament to the fact that the more she changes the more she stays the same.